What happens when we are exposed to the opposite sex hormones?

Let’s talk hormones.

Whhen adults (or children) are exposed to the hormones typically associated with the opposite sex, what happens?

Whether it’s for gender-affirming care, medical treatments, certain medical conditions, or just scientific curiosity, introducing testosterone into a body used to estrogen, or vice versa, can have some pretty bizarre effects.

Let’s break it down for each sex hormone.

Estrogen/Progesterone in People Assigned Male at Birth

When someone born with testosterone as their dominant hormone begins taking estrogen and/or progesterone (commonly as part of hormone therapy for trans women or as treatment for prostate cancer), a variety of changes occur over time:

Common physical and physiological effects:

• Breast development (gynecomastia)

• Decreased muscle mass and strength

• Softening of skin

• Slower or halted facial/body hair growth

• Shrinkage of testicles and decreased sperm production

• Reduced libido

• Mood shifts – often described as a broader emotional range

• Fat redistribution – less in the abdomen, more in the hips and thighs

Many of these changes are gradual and occur over months to years. Some, like breast growth, may become permanent even if hormone therapy is stopped.

Testosterone in People Assigned Female at Birth

When testosterone is introduced, whether for gender-affirming care, treatment of certain conditions, or (less commonly) as part of menopausal care (new but important use), it brings its own list of physiological changes:

Common effects include:

• Voice deepening (usually permanent)

• Increased facial and body hair (hirsutism)

• Increased muscle mass

• Cessation of menstruation

• Acne and oilier skin

• Clitoral enlargement

• Scalp hair thinning (male-pattern hair loss in some individuals)

• Increased libido

• Mood and energy shifts – sometimes more drive, sometimes more irritability

Like estrogen, testosterone’s effects build over time and vary by individual. Some changes are reversible if therapy is stopped, but others (like voice deepening or hair growth) may not fully revert.

Important Caveats

• Dosage and supervision matter. These hormones have real medical power and need to be managed carefully.

• Risks include: blood clots, liver strain, changes in cholesterol, cardiovascular concerns, and mood disturbances—especially if taken inappropriately or without guidance.

• Everyone’s response is different. Age, genetics, body composition, and health history all play a role in how hormones work.

Why This Matters

Hormones shape our bodies in more ways than we often realize. From voice to fat distribution to mood and libido. Understanding how hormones work across different sexes matters for anyone curious about human biology, aging, fertility, or gendered medicine.

Hormones aren’t magic. But they do have a remarkable ability to shift biology in profound (and sometimes surprising) ways.

Thank you for learning with me and as always, if you have a question feel free to ask it here or via a direct message.

What Happens When Females Are Exposed to Testosterone (YouTube)